Light fixture shield



July 26, 1966 w. c. FABBRI 3,263,071

LIGHT FIXTURE SHIELD Filed Jan. 21. 1964 5 Sheets-Sheet 1 July 26, 1966w. c. FABBRI 3,263,071

LIGHT FIXTURE SHIELD Filed Jan. 21, 1964 3 Sheets-Sheet 2 July 26, I966c. FABBRI 3,263,071

LIGHT FIXTURE SHIELD Filed Jan. 21. 1964 5 Sheets-Sheet s United StatesPatent 3,263,071 LIGHT FIXTURE SHIELD William C. Fabbri, Peabody, Mass,assignor to Smithcratt Corporation, Chelsea, Mass., a corporation ofMassachusetts Filed Jan. 21, 1964, Ser. No. 339,171 5 Claims. (Cl.240-5111) This invention relates to plastic light diifusing shields forwide model fluorescent light fixtures and in particular to a shield inwhich the cold flow sag problem is solved without the structuralcomplexity or expense as sociated with previous efforts toward sagelimination.

For a number of years now shields or lenses for elongated fluorescentfixtures have been made of plastic rather than of the heavier sheetglass set in a frame. As with the glass shields, the plastic shieldshave been supported in the standard manner by their lengthwise edges,with the widthwise edges left unsupported to allow insertion andremoval. But because the plastic in practical thicknesses is less rigidthan glass and subject to a progressive deformation commonly known ascold flow, a serious difficulty has been encountered with wide modelttixtures, e. g., fixtures of the 24 inch module, due to progressivewidthwise cold flow sagging of the shields, which eventually spoilstheir appearance.

This problem is by no means as simple of solution as might appear atfirst impression. A very basic design consideration arises out of therequirement that any such fixtures be foolproof in the sense thatanyone, regardless of how unskilled, and with no prior instruction,should be able to remove a shield from the fixture to change a bulb, andreplace the shield. Therefore, no supporting devices necessitatingspecial actuating manipulations should be employed, and movements of theshield during its installation should be very simple. Additionally, itis important that the insertion of the shield should involve movementsoccupying a minimum of vertical space in the housing.

For the above reasons, and others, the standard procedure for insertingand supporting the shield should, as far as possible, continue to beused. For this procedure, the typical shield has a length slightly lessthan the length of the housing opening and a width slightly greater thanthe width of that opening. The procedure involves sliding the shieldwidthwise up into the housing at a slight angle to the horizontal untilit extends into the housing laterally beyond its normal position so thatthe opposite lengthwise edge can be raised and clear the housing edge.Then, after the entire shield is raised into the opening, a slightlateral shifting brings the two lengthwise edges back into position torest upon the sides of the housing for support. Obviously, the aboveprocedure does not allow the use of a shield that is longer than thehousing opening.

Plastic shields for narrow model fixtures to be installed by thestandard procedure are presently made by the relatively inexpensiveextrusion or injection molding procedures in which the shield has auniform cross-section along its length. But shields for wider fixtureshave been more susceptible, of course, to widthwise sagging and as aresult it has been thought impossible to make them so economically.Rather, all of the wide model plastic shields being made today, even bythe most progressive and largest companies, are made with thecrosssection of the shield being varied along its length to give thecenter a special upwardly dished shape, either conical or pyramid-like,whereby the shield is stiffened against sagging. Because such shapes areextremely expensive, the wide shield has been many times more costlythan a shield half the same Width.

Accordingly, it is a principal object of this invention to provide a newinexpensive shield for wide fluorescent lighting fixtures having meansfor overcoming sagging and particularly one which permits formation byinexpensive techniques.

In accomplishing this object the invention "avoids the variedcross-section technique of the prior art and instead employs a novelstructure and system in no way dependent upon the cross-section or otherfeatures of the shape of the main shield body. In part, the inventionlies in discovering the usefulness of the fact that a wide shield ofsuch a thickness as to be subject to widthwise sag, when manuallysupported by grasping it in the conventional position at the center ofone of the long sides, will sag or wraok slightly but distinctlylengthwise, as well as widthwise, due to the unsupported weight of theends of the shield. This lengthwise end sagging causes the ends of theshield to draw in slightly and automatically without any specialattention by the person raising the shield. The invention takesadvantage of this phenomenon, and tab projections are employed in themiddle of the ends of the shield, which make the flattened overalllength of the shield, at the projections only, longer than the length ofthe housing opening, contrary to what has previously been thought to benecessary. The ordinary action by a person in raising the shield int-othe opening, due to the aforementioned lengthwise wracking under theinfluence of the unsupported weight of the ends of the shield, actuallycauses these projections to move inwardly sufliciently to clear the endsof the housing, and then when the person shifts the shield towards himand lets it drop into position to rest on its two long edges, the

ends of the shield receive support by these long edges, lengthwise sagor wracking is relieved, and the pro jections move outwardlysufficiently to engage the ends of the housing and thus support theedges of the shield and prevent its widthwise sagging, the shield at itsends then acting as if it were only two narrow shields coupled togetherrather than a single wide one. It is found that though cold flow stillmay occur in the middle of the shield area, this does not detract fromappearance, this latter effect being due to the fact that the casualobserver looking up to the fixture cannot detect variations fromstraightness where, as in the case at the center of a shield but not atits edges which lie next to the ceiling or housing edges, there is nostraight ref erence with which to compare it.

A preferred embodiment of the invention is set out in the followingdetailed description and drawings, in which:

FIG. 1 is a perspective view of the entire shield;

FIG. 2 is a lengthwise vertical cross-section showing the shield wrackedlengthwise due to the unsupported weight of the ends while centered inthe fixture ready to be released to final installed position; j

FIG. 3 is a view similar to FIG. 2, but with the shield in its installedposition;

FIG. 4 is an enlarged, lengthwise vertical section showing the lower endconstruction of the housing and the end of a shield in the position ofFIG. 3;

FIG. 5 is a view similar to FIG. 4, but with the shield in the positionof FIG. 2;

FIG. 6 is a horizontal section through the line 6-6 in FIG. 4;

FIG. 7 is a perspective view showing the shield partially inserted intothe fixture;

FIG. 8 is a perspective view similar to FIG. 7, with the shield fullyinstalled;

FIG. 9 is a widthwise cross-section with the shield in the position ofFIG. 2;

FIG. 10 is a widthwise cross-section with the shield in its installedposition.

Referring to the drawings, the shield shown in FIG. 1 is of the open boxtype, with elongated rectangular main body 10, downwardly and outwardlysloping sides 11, and end caps 13. Sides 11 have laterally extendingside edges 12, which edges overlap the longitudinal edges of the housingto support the shield in its installed position (FIG. 10).

While the details of the housing 20 generally are not critical, it willhave inwardly extending ledge members 23, or their equivalents, alongits lowermost longitudinal or side edges as well as ledge members 22along its lowermost end edges. The shield is of greater width than thehousing opening to allow side edges 12 of the shield to overlap sideledge members 23 when installed, as shown in FIGS. 8 and 10. On theother 'hand, the length of the shield is less than that of the housingopening so that lower edges 14 of the shield end caps 13 will beadjacent to, but will not overlap end ledge members 22, as shown inFIGS. 3, 4, and. 8.

According to the invention, tab projections 15 of much less width W(FIG. 6) than that of the shield extend lengthwise outwardly from endcaps 13 in a generally horizontal manner, said projections 15 locatedapproximately midway between sides 11 of the shield, and just abovelower edges 14. The overall length of the shield, through theprojections, when the shield is flattened, is greater than the length ofthe housing opening, while the overall length of the shield, through allother locations, is less than the length of the opening. When the shieldis installed in the fixture, projections 15 will overlap ledge members22 of the housing. In this manner, cold flow sag along the end edges 14is eliminated. At the same time, due to the location of projections 15above edges 14, said edges 14 align with ledge portions 22, thus givinga flush transition between the shield and the housing end plates andimproving the appearance from below, as best shown in FIGS. 3 and 4.

The main body of the shield can have a uniform widthwise cross-sectionthroughout its length and can be formed as a simple linear extrusion andpractical thickness of plastic. Shield end caps 13 will normally bemanufactured separately from the main body and sides of the shield, andthen cemented or otherwise secured in position.

To install the shield, it is grasped centrally along one side as shownin FIG. 7, and the opposite side is inserted into the fixture, laterallybeyond its final position (see FIG. 9). Automatically the shieldundergoes lengthwise wracking, because the weight of the ends is notsupported, at least along the one side being grasped, and this wrackingdraws the projections 15 inwardly sufiiciently close together that theoverall length of the shield, through the projections, becomes less thanthe length of the housing opening, so that as the grasped side of theshield is swung up into the fixture, the projections easily clear ledgemembers 15, as shown in FIGS. 2 and 5. The shield is then shiftedlaterally to center the shield, and bring edges 12 over ledge members 23(FIG. 9). As the shield is lowlered to rest on members 23 (FIG. 10), theupward force on the shield becomes uniformly distributed along both longedges 12 and the wracking disappears, with the result that projections15 move apart to their installed position above ledge members 22, shownin FIGS. 3, 4 and 6.

It will be noted that the movements required to install the shieldoccupy very little vertical space; hence, bulbs 2.4 may be located closeabove the shield. To remove the shield from the fixture, the process issimply reversed.

More particularly, in the specific embodiment illustrated, the overalllength of the shield, exclusive of the projections, is 46 inches, withthe overall width belng 23 inches. The main body comprises acrylicplastic extruded 0.120 inch thick. The tab projections extend outwardlyfrom the shield end caps by Ms inch and overlap ledge member 22, wheninstalled, by an amount varying from A inch to about inch. The outermostedge of the tab is /1 inch wide and the sides of the tab extend inwardlytoward the end cap at a 30 taper. All upper edges of the tab are roundedwith a inch radius to a d in the installation process. The thickness ofthe tab 1s A; inch. I

Although the invention has been described in the context of a shieldsupported along its longitudinal edges through overlap with the housing,it is by no means limited to such a context, being applicable to anyshield supported along one pair of opposite edges and generally freealong its other edges.

What is claimed is: I

1. A flexible wide model rectangular light diffusing shield adapted tobe suspended in a bottom opening of a light fixture housing by sidesupporting means cooperatin g with the sides of the shield,

said shield having tab projections located on its ends and said fixturehaving inwardly extending ledge members located at the ends of saidhousing, said projections, when said shield is installed, extending overand resting upon said ledge members to support the ends of said shield,said shield having a length exclusive of said projections slightlyshorter than the length of the housing opening between said ledgemembers, said projections located. spaced substantially from both sidesof the shield to divide widthwise the ends of the shield into aplurality of unsupported segments each substantially narrower than thewidth of said shield,

said shield adapted to be installed while supported at its middle, theunsupported ends of said shield causing said shield to automaticallywr-ack lengthwise to allow said projections to pass upwardly beyond saidledge members, said wracking disappearing as said grasped side is leftto rest upon said side supporting means.

2. The shield of claim 1 in which there are two of said tab projections,one located on each end of said shield substantially centrallywidthwise.

3. The shield of claim 1 in which said tab projections have asubstantially small widthwise extent relative to the width of said.shield.

4. The wide model rectangular plastic light diffusing shield of claim 1wherein said shield has a width greater than the width of the housingopening, the sides of said shield overlapping and resting upon the sidesof said housing opening when said shield is installed.

5. A flexible Wide model rectangular plastic light diffusing shieldadapted to be suspended in an open bottomed housing having inwardlyextending ledge members along its lowermost side and end edges,

said shield having a width greater than the width of the housing openingbetween its side ledge members, the sides of said shield overlapping andresting upon said side ledge members when said shield is installed,

said shield having tab projections on its ends, said pmjections, whensaid shield is installed, extending laterally over and resting upon saidend ledge members,

said shield having a length exclusive of said projecto Wrack lengthwiseto allow said projections to pass tions slightly shorter than the lengthof said housing upwardly beyond the end ledge members of said openingbetween its end ledges, said projections therehousing, said Wrackingdisappearing as said grasped by dividing widthwise the ends of saidshield into side is left to rest upon said ledge members. unsupportedsegments each substantially shorter than 5 h id h of id hi ld,References Cited by the Examiner said projections located centrallywidthwise on the ends UNITED STATES PATENTS of said shield and spacedupwardly from the lowermost edges of said shield ends, said shield endsthere- 315830O 11/1964 Van Steenhoven IMG 5111 X by being adapted toabut said end ledge members 10 3192381 6/1965 Zurawski et 240*5111 Xwhen said shield is installed, said shield adapted to be installed Whilegrasped at the NORTON ANSHER P'zmary Exammer' middle of one of itssides, the unsupported ends of C. R. RHODES, Assistant Examiner. saidgrasped side causing said shield automatically

1. A FLEXIBLE WIDE MODEL RECTANGULAR LIGHT DIFFUSING SHIELD ADAPTED TOBE SUSPENDED IN A BOTTOM OPENING OF A LIGHT FIXTURE HOUSING BY SIDESUPPORTING MEANS COOPERATING WITH THE SIDES OF THE SHIELD, SAID SHIELDHAVING TAB PROJECTIONS LOCATED ON ITS ENDS AND SAID FIXTURE HAVINGINWARDLY EXTENDING LEDGE MEMBERS LOCATED AT THE ENDS OF SAID HOUSING,SAID PROJECTIONS, WHEN SAID SHIELD IS INSTALLED, EXTENDING OVER ANDRESTING UPON SAID LEDGE MEMBERS TO SUPPORT THE ENDS OF SAID SHIELD, SAIDSHIELD HAVING A LENGTH EXCLUSIVE OF SAID PROJECTIONS SLIGHTLY SHORTERTHAN THE LENGTH OF THE HOUSING OPENING BETWEEN SAID LEDGE MEMBERS, SAIDPROJECTIONS LOCATED SPACED SUBSTANTIALLY FROM BOTH SIDES OF THE SHIELDTO DIVIDE WIDTHWISE THE ENDS OF THE SHIELD INTO A PLURALITY OFUNSUPPORTED SEGMENTS EACH SUBSTANTIALLY NARROWER THAN THE WIDTH OF SAIDSHIELD, SAID SHIELD ADAPTED TO BE INSTALLED WHILE SUPPORTED AT ITSMIDDLE, THE UNSUPPORTED ENDS OF SAID SHIELD CAUSING SAID SHIELD TOAUTOMATICALLY WRACK LENGTHWISE TO ALLOW SAID PROJECTIONS TO PASSUPWARDLY BEYOND SAID LEDGE MEMBERS, SAID WRACKING DISAPPEARING AS SAIDGRASPED SIDE IS LEFT TO REST UPON SAID SIDE SUPPORTING MEANS.